1. Field of the Invention
The present invention relates to a camera system such as an SLR camera system which includes a camera body and an interchangeable lens that is detachably attached to the camera body, and in particular relates to a diaphragm driving device of the camera system which is configured so that the operation of an adjustable diaphragm of the interchangeable lens is controlled by the camera body.
2. Description of the Prior Art
In conventional camera systems using an interchangeable photographic lens (hereinafter referred to as an interchangeable lens), especially in SLR camera systems, upon taking a picture, the main mirror (quick-return mirror) is raised so that it retracts from a photographing optical path while a diaphragm drive mechanism in the camera body is actuated to stop down a diaphragm (iris diaphragm) to the position of a preset F-number from a full-aperture state, and thereupon, the shutter (focal-plane shutter) is released. For instance, the camera body is provided with a diaphragm-driving slide plate while the interchangeable lens is provided with a diaphragm control bar which engages with the diaphragm-driving slide plate when the interchangeable lens is mounted to the camera body, wherein the diaphragm-driving slide plate moves in association with the upward retracting movement of the main mirror that is caused by the mirror drive mechanism, the diaphragm control bar operates to make the diaphragm in the interchangeable lens perform a stop-down operation, and the diaphragm-driving slide plate is slidingly moved by an amount of movement (stroke) corresponding to a preset exposure (F-number) concurrently with the aforementioned upward retracting movement of the main mirror to thereby move the diaphragm control bar to stop down the diaphragm of the interchangeable lens. In the interchangeable lens, the diaphragm control bar is continuously biased in a direction to stop down the diaphragm by a control-bar restoring spring (extension spring) provided in the interchangeable lens, and the diaphragm control bar is forced to move to a full-aperture position against the biasing force of the control-bar restoring spring via the engagement of the diaphragm control bar with the diaphragm-driving slide plate when the interchangeable lens is mounted to the camera body. Upon taking a picture, a movement of the diaphragm-driving slide plate causes the diaphragm control bar to move in a direction to stop down the diaphragm by utilizing the biasing force of the control-bar restoring spring. Additionally, a new type of diaphragm driving device which drives a diaphragm drive motor installed in a camera body and transfers the rotational driving force of the diaphragm drive motor to the interchangeable lens to drive the diaphragm in the interchangeable lens has been proposed in recent years as shown in Japanese Unexamined Patent Publication No. 2002-290828.
The diaphragm driving device shown in JUPP 2002-290828 is required to be equipped with a mechanism for coupling a diaphragm drive motor installed in the camera body to a stop-down mechanism installed in the interchangeable lens, and therefore cannot be applied to an interchangeable lens equipped with a conventional diaphragm control bar, thus having a problem with general versatility. On the other hand, the diaphragm driving device which stops down the diaphragm of the interchangeable lens by a conventional diaphragm-driving slide plate excels in general versatility with interchangeable lenses, but there is a problem with the power consumption for driving the diaphragm drive motor increasing since the diaphragm-driving slide plate, provided in the camera body for driving the diaphragm control bar installed in the interchangeable lens, is driven by a rotational force of the diaphragm drive motor (stepping motor). Namely, in conventional interchangeable lenses, since the spring constant (spring force) of the control-bar restoring spring that is associated with the diaphragm control bar differs according to the type of interchangeable lens, the driving current for the diaphragm drive motor (stepping motor), that serves as a drive source for the diaphragm-driving slide plate, is determined so that the diaphragm drive motor (stepping motor) can drive an interchangeable lens in which the spring force of the control-bar restoring spring is set to a minimum. Due to this setting, the driving force of the diaphragm drive motor (stepping motor) needs to be increased as the spring force of the control-bar restoring spring is reduced since a combination of the spring force of the control-bar restoring spring and the driving force of the diaphragm drive motor (stepping motor) drives the diaphragm-driving slide plate while resiliently deforming (extending) the control-bar restoring spring in the camera body against the biasing force thereof. Conversely, if the spring force of the control-bar restoring spring is great, the driving force of the diaphragm drive motor (stepping motor) can be reduced. However, in conventional diaphragm driving devices, the driving force of the diaphragm drive motor (stepping motor) must be set relatively large on the assumption that an interchangeable lens with a control-bar restoring spring whose spring force is small may be mounted to the camera body. Therefore, if the spring force of the control-bar restoring spring is great, the electrical power which is supplied to the stepping motor becomes greater than necessary, which results in an unnecessary increase in power consumption.